I concur with this analysis. My car seems to be a much nicer beast to drive and the main thing is the noise which was worrisome before is now a lot less..
turbo/intake whine..?
- Thread starter 08_MS3_GT
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I concur with this analysis. My car seems to be a much nicer beast to drive and the main thing is the noise which was worrisome before is now a lot less..
i am as of right now. i may experiment with 1 or zero shims, but not at the present time.
Forge BPV analysis
I have had an interesting evening. I decided to try to understand the springs/shims in the Forge BPV, but I must say I know a lot more details, but I am not sure it is going to help much.
I set up my hand vacuum pump and vacuum gauge so I could suck on the valve manifold nipple and observe the piston moving. I checked out the stock valve first, and then tried every combination of yellow spring, 0, 1, & 2 shims, blue spring, 0, 1, & 2 shims, and just for giggles, the red spring with 0 and 1 shims. I repeated each of the measurements on the yellow and blue springs four times, going through each combination to check for consistency. Man that was a lot of opening and closing the cover and shuffling springs around.
First an observation of the construction of the stock VS. the Forge BPV. I did not disassemble the stock valve, but I am almost certain it is simply a diaphram with the manifold vacuum on one side, the boosted air on the other, and a preloaded spring holding it closed. The valve seems to open quite linearly with the pressure differential. Also, it doesn't open very far.
The Forge design is much cleverer. When the valve is closed, the manifold vacuum acts on the top of the piston, about 1.5" in diameter. The boosted air acts on the closed piston which is about .75" in diameter. This means that the vacuum has four times the effect on the piston than the boost pressure. Now, when the valve begins to open, the boost pressure is allowed inside the valve and now acts on the full 1.5" in diameter. The effect of this is when the pressure differential reaches the point where the valve starts to open, it opens quickly because of the assist from the boost pressure. It starts to open later though, because the boost pressure is not exerting as much pressure against the preload of the spring.
Is this making sense?
Anyway, here are the numbers:
The stock valve starts to open at 7.8 psi, and is fully open (which isn't very open) at 13.8 psi.
The Forge valve starts to open, and is fully open like this:
Yellow, 0 shims - start 4.6, full 7.0
Yellow, 1 shim - start 5.0, full 7.6
Yellow, 2 shims - start 5.5, full 8.4
Blue, 0 shims - start 4.3, full 7.5
Blue, 1 shim - start 5.3, full 7.9
Blue, 2 shims - start 6.1, full 9.1
Red, 0 shims - start 7.5, full 13.3
Red, 1 shim - start 8.5, full 13.8
Observations:
1) The yellow with no shims opens at a higher pressure then the blue with no shims, but this is because at least in my set, the yellow spring is longer than the blue one, so starts with higher preload for the same height. This points out that the resting length of the spring has a significant effect on the opening point and there may be manufacturing tolerences here so yours may be different than mine.
2) The stock valve in free air starts to open at 7.8 psi, where for the Forge to start to open at that point, you would have to run the red spring, which has been shown to be much too strong. This blows my idea out of the water - you cannot adjust the spring preload by comparing the simple opening vacuum on the intake manifold the same as the stock valve. The construction of the valves is so different, this just doesn't work.
My conclusion is that to adjust the valve properly, you need to put a boost gauge on the boost tube just before the throttle butterfly. You want to adjust the valve preload so it opens just as you close the throttle from WOT with only a small boost spike as that happens. In my opinion you want as light a spring as possible to keep the valve open as long as you can until you get into the thottle again so the turbo keeps free-wheeling.
I am now even more convinced the the ideal BPV is electrically operated, bang open and bang closed, based on electronic reading of the throttle plate position and boost pressure.
Sorry for the pedantic long-windedness, but I got into it and couldn't stop...
I'm out to the garage to put my car back together - I'm gonna try yellow spring and one shim for tomorrow's test drive (um commute).
I have had an interesting evening. I decided to try to understand the springs/shims in the Forge BPV, but I must say I know a lot more details, but I am not sure it is going to help much.
I set up my hand vacuum pump and vacuum gauge so I could suck on the valve manifold nipple and observe the piston moving. I checked out the stock valve first, and then tried every combination of yellow spring, 0, 1, & 2 shims, blue spring, 0, 1, & 2 shims, and just for giggles, the red spring with 0 and 1 shims. I repeated each of the measurements on the yellow and blue springs four times, going through each combination to check for consistency. Man that was a lot of opening and closing the cover and shuffling springs around.
First an observation of the construction of the stock VS. the Forge BPV. I did not disassemble the stock valve, but I am almost certain it is simply a diaphram with the manifold vacuum on one side, the boosted air on the other, and a preloaded spring holding it closed. The valve seems to open quite linearly with the pressure differential. Also, it doesn't open very far.
The Forge design is much cleverer. When the valve is closed, the manifold vacuum acts on the top of the piston, about 1.5" in diameter. The boosted air acts on the closed piston which is about .75" in diameter. This means that the vacuum has four times the effect on the piston than the boost pressure. Now, when the valve begins to open, the boost pressure is allowed inside the valve and now acts on the full 1.5" in diameter. The effect of this is when the pressure differential reaches the point where the valve starts to open, it opens quickly because of the assist from the boost pressure. It starts to open later though, because the boost pressure is not exerting as much pressure against the preload of the spring.
Is this making sense?
Anyway, here are the numbers:
The stock valve starts to open at 7.8 psi, and is fully open (which isn't very open) at 13.8 psi.
The Forge valve starts to open, and is fully open like this:
Yellow, 0 shims - start 4.6, full 7.0
Yellow, 1 shim - start 5.0, full 7.6
Yellow, 2 shims - start 5.5, full 8.4
Blue, 0 shims - start 4.3, full 7.5
Blue, 1 shim - start 5.3, full 7.9
Blue, 2 shims - start 6.1, full 9.1
Red, 0 shims - start 7.5, full 13.3
Red, 1 shim - start 8.5, full 13.8
Observations:
1) The yellow with no shims opens at a higher pressure then the blue with no shims, but this is because at least in my set, the yellow spring is longer than the blue one, so starts with higher preload for the same height. This points out that the resting length of the spring has a significant effect on the opening point and there may be manufacturing tolerences here so yours may be different than mine.
2) The stock valve in free air starts to open at 7.8 psi, where for the Forge to start to open at that point, you would have to run the red spring, which has been shown to be much too strong. This blows my idea out of the water - you cannot adjust the spring preload by comparing the simple opening vacuum on the intake manifold the same as the stock valve. The construction of the valves is so different, this just doesn't work.
My conclusion is that to adjust the valve properly, you need to put a boost gauge on the boost tube just before the throttle butterfly. You want to adjust the valve preload so it opens just as you close the throttle from WOT with only a small boost spike as that happens. In my opinion you want as light a spring as possible to keep the valve open as long as you can until you get into the thottle again so the turbo keeps free-wheeling.
I am now even more convinced the the ideal BPV is electrically operated, bang open and bang closed, based on electronic reading of the throttle plate position and boost pressure.
Sorry for the pedantic long-windedness, but I got into it and couldn't stop...
I'm out to the garage to put my car back together - I'm gonna try yellow spring and one shim for tomorrow's test drive (um commute).
That was an extremely informative post yet I'm more confused than ever. Thanks for experimenting with the settings and posting your findings.
I find it interesting that the yellow with 1 or 2 shims both starts to open and is fully open at a higher PSI than the blue with no shims (according to your findings). This might reinforce the idea that the yellow + 2 shims is the best for our cars. I'd like to hear Forge's stance on this.
I find it interesting that the yellow with 1 or 2 shims both starts to open and is fully open at a higher PSI than the blue with no shims (according to your findings). This might reinforce the idea that the yellow + 2 shims is the best for our cars. I'd like to hear Forge's stance on this.
Very nice write up Rotus 8. Ha ha whats funny is I am actually a Valve Engineer, I am already thinking about designing my own BPV for grins and giggles. Essentially this type of valve is a Piston Check Valve.
The only problem I have here is that it DOES only simulate one side. It is very difficult to know exactly how the boost pressure is effecting it on the other side.
I am running as I stated yellow with two shims and everything was fine for a few days, then last night I seemed to be getting some surge again as it got colder. So I am thinking about going down to one shim or zero shims for the winter and two in the summer. Do you think we could be effected my seasons?
It is also strange though that the stock BPV seems to most closely match the RED Spring with 1 Shim. But then again maybe its not. There is a difference in the surface area that sees boost between the Stock and the Forge right?
Force = Pressure / Area;
I know for sure the I.D. of the vacuum side of the Forge is bigger than the stock one, therefore it would take MORE vacuum to make it open.
So if the Stock BPV has a smaller surface area on the piston at the same pressure this would result in a bigger force. The Forge has a dished piston if I remember correctly.
Anyway I made a graph, cause I was bored and its interesting what it shows. I think the blue with No shims may of been an anomaly as its the only one that isnt linear. Also look at the huge jump on the Red Spring.
The only problem I have here is that it DOES only simulate one side. It is very difficult to know exactly how the boost pressure is effecting it on the other side.
I am running as I stated yellow with two shims and everything was fine for a few days, then last night I seemed to be getting some surge again as it got colder. So I am thinking about going down to one shim or zero shims for the winter and two in the summer. Do you think we could be effected my seasons?
It is also strange though that the stock BPV seems to most closely match the RED Spring with 1 Shim. But then again maybe its not. There is a difference in the surface area that sees boost between the Stock and the Forge right?
Force = Pressure / Area;
I know for sure the I.D. of the vacuum side of the Forge is bigger than the stock one, therefore it would take MORE vacuum to make it open.
So if the Stock BPV has a smaller surface area on the piston at the same pressure this would result in a bigger force. The Forge has a dished piston if I remember correctly.
Anyway I made a graph, cause I was bored and its interesting what it shows. I think the blue with No shims may of been an anomaly as its the only one that isnt linear. Also look at the huge jump on the Red Spring.
Um, no. Force = Pressure * Area.
And yes, the back side design effects the operation in a big way, but I don't know enough to simulate it. To do this experimentally, I would have to build a plenum with controlled pressure on the boost side, but i am not that energetic. When the valve is closed, the small diameter of the piston is exposed to boost pressure, plus the reset of the backside is exposed to atmospheric pressure (or close) through the bypass hose.
My test drive this morning with yellow spring and one shim felt just fine. I'll hook up the OBDII logger on the way home and record boost pressure for a more objective evaluation.
Well, just to report, with four test drives under my belt (every commute's a track day!), I am happy with the yellow spring with one shim. Of course this is on my car with my particular valve and spring, YMMV.
I am in the process of installing some more instrumentation in the car over the next couple of weeks and I hope to be able to log the pressure in the pipe before the throttle plate. This will allow better evaluation of the BPV operation and more informed adjusting.
I am in the process of installing some more instrumentation in the car over the next couple of weeks and I hope to be able to log the pressure in the pipe before the throttle plate. This will allow better evaluation of the BPV operation and more informed adjusting.
the more effective function of the yellow spring is certainly confirmed by now, given that we've all had good experience with it. any conjecture as to which shim configuration (zero, one, two) would be best?
i've been enjoying the technical conversation going on (thumb). i can't really contribute much since my background/education hasn't involved pressure relieving systems such as these. i know much more about how to size valves that are used for emergency situations in chemicals processing, which isn't really relevant for diverter valves.
Yeah, it does feel good to have a somewhat worthwhile thread that doesnt result in everybody crashing and burning from the flaming going back and forth.
I am going to try Yellow with one shim, hopefully sometime this weekend, although the R6 may be getting a caning if the weather is nice tommorow...lets hope its not snowing in Houston again
I am going to try Yellow with one shim, hopefully sometime this weekend, although the R6 may be getting a caning if the weather is nice tommorow...lets hope its not snowing in Houston again
patty AT forge
Member
F430tech,
You have me a bit confused here:
"I know for sure the I.D. of the vacuum side of the Forge is bigger than the stock one, therefore it would take MORE vacuum to make it open.
So if the Stock BPV has a smaller surface area on the piston at the same pressure this would result in a bigger force. The Forge has a dished piston if I remember correctly."
A larger surface area will net a greater amount of force whether from a positive or negative pressure differential.
You have me a bit confused here:
"I know for sure the I.D. of the vacuum side of the Forge is bigger than the stock one, therefore it would take MORE vacuum to make it open.
So if the Stock BPV has a smaller surface area on the piston at the same pressure this would result in a bigger force. The Forge has a dished piston if I remember correctly."
A larger surface area will net a greater amount of force whether from a positive or negative pressure differential.
As Rotus 8 so kindly corrected Force = Pressure*Area
What I meant was the stock valve has a smaller surface area because its not dished therefore to achieve the same force the pressure pushing on the stock valve would have to be bigger correct?
I do know that when you push on the STOCK BPV its very hard to push.
Essentially its the sum of both the boost pressure and vacuum sucking on the backside that overcome the spring right? Also when you push on the stock valve it doesnt just spring back closed, its dampened. We make piston check valves with this feature to STOP them from slamming shut, maybe there is something to be had in that.
What I meant was the stock valve has a smaller surface area because its not dished therefore to achieve the same force the pressure pushing on the stock valve would have to be bigger correct?
I do know that when you push on the STOCK BPV its very hard to push.
Essentially its the sum of both the boost pressure and vacuum sucking on the backside that overcome the spring right? Also when you push on the stock valve it doesnt just spring back closed, its dampened. We make piston check valves with this feature to STOP them from slamming shut, maybe there is something to be had in that.
